Before the approval of Proposition 13, the constitution limited taxes on property to 1% of the full cash value of the property. "Full cash value" is defined in the constitution as the appraised value of that real property when purchased, newly constructed, or a change of ownership has occurred.

The California Constitution excluded from classification as “newly constructed” the cost of re-constructing or improving a building to comply with any local ordinances that related to earthquake safety. The California Constitution also authorized the Legislature to exclude from classification as “newly constructed” the construction or installation in existing buildings of certain seismic retrofitting improvements or improvements utilizing earthquake hazard mitigation technologies.

SCA 4 (Proposition 13) changed the law by excluding from the definition of “newly constructed” the portion of an existing structure that consists of the construction or reconstruction of seismic retrofitting components, as defined by the Legislature. Proposition 13 deleted the previous exclusion for structures constructed of unreinforced masonry bearing wall construction, and the existing grant of authority to the Legislature to exclude certain seismic retrofitting improvements or improvements utilizing earthquake hazard mitigation technologies.

Supporters

Key supporters of Proposition 13 included Roy Ashburn, Tom Bordonaro and Barbara Alby. Bordonaro, who is the county assessor for San Luis Obispo County and Alby, who is the Chief-Deputy Board Member for District 2 of the Board of Equalization, signed the official voter's guide arguments in favor of Proposition 13, along with Senator Ashburn.

The Green Party of Alameda County recommended[1] a "no" vote on Proposition 13, saying that they don't trust its only listed sponsor, conservative Republican State Senator Ray Ashburn, that its primary purpose may be to provide a tax break to corporate property owners who did seismic retrofits more than 15 years ago, and that the measure is too complex to understand its effects.

Editorial opinion

"Vote Yes"

The editorial board of the Contra Costa Times encouraged its readers to vote "yes" on Proposition 13, writing, "Proposition 13 on the June 8 ballot is a technical, but important correction to assessments of properties that are retrofitted to make them more resistant to earthquakes."[4]

The editorial board of the San Luis Obispo Tribune endorsed a "yes" vote, saying, "We wish the state could provide more financial incentives to make retrofitting less burdensome, but in this awful economy, that’s simply not possible. Proposition 13 would at least provide some long-term tax relief for property owners who are trying to do the right thing by making their buildings safer. We strongly urge a yes vote on the measure.[5]

The San Francisco Chronicle's editorial board was in favor, saying, "In California's divisive politics, it's a miracle to find a ballot measure that has broad support, clear benefits and no identifiable opposition. That's the case for state Proposition 13, a measure that encourages seismic upgrades to quake-prone buildings by canceling the risk of increased property taxes."[6]

The Los Angeles Times was in favor, saying, "With these thorny questions down the ballot, voters can feel some sense of relief that the first measure they'll be confronted with is straightforward and easy to support...It's as close as a California ballot measure comes to being a no-brainer."[7]

The Orange County Register was in favor, saying, "Recent earthquakes killing many people in Haiti and Chile – and that 7.2-magnitude quake in Baja on April 4 that also shook Orange County – are reminders of the need for strong buildings. It doesn't make sense to punish homeowners and businesses that want to improve their buildings' quality."[8]

The (Petaluma) Press Democrat: "State measure offers incentive to prepare for an earthquake".[9]

The Marin Independent-Journal: "If it will help encourage owners to make their properties safer, the exemption is worth it."[10]

The Lompoc Record: "We firmly believe property values should be evaluated on a regular basis, but if approving Proposition 13 increases the probability of getting buildings in better shape to withstand the forces of an earthquake, we are in favor of it."[11]